The present invention relates to methods and apparatuses for automated manufacture of reclosable plastic packages having a resealable closure, especially as part of a form, fill and seal process.
In the use of plastic bags and packages, particularly for foodstuffs, it is important that the bag be hermetically sealed until the purchaser acquires the product, takes it home, and opens the bag or package for the first time. It is then commercially attractive and useful for the consumer that the bag or package be reclosable so that its contents may be protected. Flexible plastic zippers have proven to be excellent for reclosable bags, because they may be manufactured with high-speed equipment and are reliable for repeated reuse.
A typical zipper comprises one fastener strip or closure member having a groove and attached to one side of the bag mouth, and another fastener strip or closure member having a rib and attached to the other side of the bag mouth, which rib may interlock into the groove when the sides of the mouth of the bag are pressed together. Alternatively, a fastener strip having a plurality of ribs may be on one side of the bag mouth, while a fastener strip having a plurality of grooves or channels may be on the other side, the ribs locking into the channels when the sides of the mouth of the bag are pressed together. In the latter case, there may be no difference in appearance between the two fastener strips, as the ribs may simply be the intervals between channels on a strip that lock into another of the same kind. In general, some form of male/female interengagement is used to seal the two sides of the bag mouth together. The fastener strips or closure members are bonded in some manner to the material from which the bags themselves are manufactured.
In the automated manufacture of plastic reclosable packages or bags, it is known to feed a zipper assembly to a position adjacent a sheet of thermoplastic film and then attach the zipper assembly to the bag by means of heat sealing. The zipper assemblies are attached at spaced intervals along the thermoplastic sheet, one zipper assembly being attached to each section of film respectively corresponding to an individual package or bag. The zipper assembly consists of two interlocking fastener strips that typically lie inside the mouth of the package. Each fastener strip preferably has a zipper flange that extends toward the product side of the package in a direction transverse to the line of the zipper. In accordance with one known method of feeding zipper assemblies to an automated form, fill and seal machine, the zipper assembly is in the form of a tape that is unwound from a spool for automated feeding. The tape comprises a continuous length of interlocked fastener strips. The continuous tape is fed to a cutting device that cuts the tape at regular lengths to form an individual zipper. Each individual zipper is then attached to the thermoplastic bag making film by heat sealing or other suitable means. Then the package is formed, filled and sealed on a form-fill-seal (FFS) machine.
Other types of reclosable plastic bags, however, contain a slider that facilitates a consumer opening and re-closing the package by disengaging and re-engaging the two sides of the zipper together. Slide-zipper assemblies are well known in the reclosable packaging art. Conventional slider-operated zipper assemblies typically comprise a plastic zipper having two interlocking profiles and a slider for opening and closing the zipper. In one type of slider-operated zipper assembly, the slider straddles the zipper and has a separating finger at one end that is inserted between the profiles to force them apart as the slider is moved along the zipper in an opening direction. The other end of the slider is sufficiently narrow to force the profiles into engagement and close the zipper when the slider is moved along the zipper in a closing direction. Other types of slider-operated zipper assemblies avoid the use of a separating finger. For example, U.S. Pat. No. 6,047,450 discloses a zipper comprising a pair of mutually interlockable profiled structures and having an A-shaped profile. Portions of the two profiled structures form a fulcrum about which the profiled structures may be pivoted when the slider forces lower edges of the bases towards each other. Above the fulcrum point, the interlocked male and female profiles disengage, thereby opening the zipper. The path of the slider as blocked at opposing sealed ends of the zipper halves by slider end stops, which are typically formed by ultrasonically stomping.
Whether or not the zipper assembly is opened and closed by a slider, the zipper flanges of the zipper assembly, when sealed to the bag making film, must not be sealed to each other. Such xe2x80x9cseal-throughxe2x80x9d of the zipper flanges makes the bag difficult to open and susceptible to losing its reclosability, for example, if the bag film were to be torn during pulling apart of the sealed flanges.
Some techniques for avoiding xe2x80x9cseal-throughxe2x80x9d of the zipper flanges include: inserting an insulating separator plate between the zipper flanges prior to heat sealing the flanges to the bag making film; and constructing the zipper flanges to have confronting layers of high-melting-point thermoplastic material that does not soften during sealing. The use of separator plates is suited more to instances where the zipper assembly is applied to the bag making film in the machine direction, since transverse application would require that the separator plate be repeatedly inserted between the zipper flanges and then retracted. The manufacture of zipper assemblies in which each flange comprises a layer of high-melting-point thermoplastic material laminated to a layer of low-melting-point thermoplastic sealant material is more costly than the manufacture of zipper assemblies without laminated flanges.
U.S. Pat. No. 6,327,837 discloses a zipper assembly having one flange longer than the other. In this case the zipper assembly is initially attached to the bag making film by sealing the portion of the long flange that extends beyond the short flange to the bag making film.
There is a need for an alternative method for automated application of zipper assemblies to bag making film without flange xe2x80x9csealthroughxe2x80x9d.
The present invention is directed to automated reclosable packaging manufacturing equipment for applying zipper tape to bag making film, especially as part of a form-fill-seal process. The invention is also directed to a method of joining a zipper flange of a zipper assembly to bag making film without xe2x80x9cseal-throughxe2x80x9d of the zipper flanges.
One aspect of the invention is a method of making a zippered bag, comprising the following steps: (a) pressing a web of bag making film and first and second zipper flanges of a zipper assembly together along the length of the zipper assembly, with the first zipper flange sandwiched between and in contact with the web of bag making film and the second zipper flange; (b) during step (a), causing heat to be conducted through the web of bag making film into the first zipper flange, the amount of heat conducted through the web of bag making film being sufficient to seal the web of bag making film to the first zipper flange in a first seal without sealing the first zipper flange to the second zipper flange; (c) subsequent to step (b), folding the web of bag making film and sealing the folded web to form a bag having a mouth with the first seal disposed on and running the length of one side of the mouth; (d) pressing opposing walls of the bag and the first and second zipper flanges together along the length of the zipper assembly, with the second zipper flange sandwiched between and in contact with a folded-over portion of the web of bag making film and the first zipper flange; and (e) during step (d), causing heat to be conducted through the folded-over portion of the web of bag making film into the second zipper flange, the amount of heat conducted through the folded-over portion of the web of bag making film being sufficient to seal the folded-over portion of the web of bag making film to the second zipper flange in a second seal without sealing the first zipper flange to the second zipper flange. The second seal is disposed on and runs the length of the other side of the mouth of the bag.
Another aspect of the invention is a system for making a zippered bag comprising: first means for pressing a web of bag making film and first and second zipper flanges of a zipper assembly together along the length of the zipper assembly, with the first zipper flange sandwiched between and in contact with the web of bag making film and the second zipper flange; first means for causing heat to be conducted through the web of bag making film into the first zipper flange during pressing, the amount of heat conducted through the web of bag making film being sufficient to seal the web of bag making film to the first zipper flange in a first seal without sealing the first zipper flange to the second zipper flange; means for folding and sealing the web of bag making film with attached zipper assembly to form a bag having a mouth with the first seal disposed on and running the length of one side of the mouth; second means for pressing opposing walls of the bag and the first and second zipper flanges together along the length of the zipper assembly, with the second zipper flange sandwiched between and in contact with a folded-over portion of the web of bag making film and the first zipper flange; and second means for causing heat to be conducted through the folded-over portion of the web of bag making film into the second zipper flange, the amount of heat conducted through the folded-over portion of the web of bag making film being sufficient to seal the folded-over portion of the web of bag making film to the second zipper flange in a second seal without sealing the first zipper flange to the second zipper flange. The second seal is disposed on and runs the length of the other side of the mouth of the bag.
A further aspect of the invention is a method of making reclosable bags having a zipper assembly comprising first and second profiled closure members, and first and second zipper flanges respectively connected to the first and second closure members and extending generally parallel therefrom. The method comprises the following steps: (a) placing one side of the zipper assembly in contact with a length of bag making film, a first portion of the first zipper flange having one side confronting a first portion of the length of bag making film and the other side confronting a first portion of the second zipper flange; (b) sealing the first portion of the first zipper flange to the first portion of the length of bag making film while the first portion of the first zipper flange and a first portion of the second zipper flange are in contact, thereby forming a first seal without sealing the second zipper flange to the first zipper flange; (c) making the length of bag making film into a receptacle having a mouth, wherein the first portion of the length of bag making film forms one half of the mouth and a second portion of the length of bag making film, generally opposite to the first portion, forms the other half of the mouth; and (d) sealing a second portion of the second zipper flange to the second portion of the length of bag making film while the second portion of the second zipper flange is in contact with a second portion of the first zipper flange, thereby forming a second seal without sealing the second zipper flange to the first zipper flange. The first seal is produced by heat that is conducted through the first portion of the length of bag making film and then into the first zipper flange, and the second seal is produced by heat that is conducted through the second portion of the length of bag making film and then into the second zipper flange.
Another aspect of the invention is a system for manufacturing reclosable bags comprising: a vertical form-fill-seal (VFFS) machine for forming, filling and sealing a reclosable bag, comprising a forming collar, a fill tube and sealing means; a roll of bag making film comprising a wound portion and an unwound portion, the unwound bag making film extending from the wound portion of the roll to the forming collar and through the vertical FFS machine; opposing grooved elements comprising grooves designed to hold interlocked first and second closure members of a zipper assembly while first and second zipper flanges of the zipper assembly project in a forward machine direction, the first zipper flange being disposed between unwound bag making film and the second zipper flange; first and second sealing bars arranged in opposition at a first sealing station with the first sealing bar above the second zipper flange and the second sealing bar below the unwound bag making film; means for moving the first and second sealing bars between respective extended positions and respective retracted positions, the first and second zipper flanges and a first portion of unwound bag making film being pressed between the first and second sealing bars in their respective extended positions; first control means for heating the second sealing bar while in its extended position, the first sealing bar being unheated while in its extended position, and the second sealing bar being heated to a degree that the first zipper flange is sealed to the first portion of unwound bag making film without the first zipper flange being sealed to the second zipper flange; and means for advancing the bag making film with the zipper assembly attached thereto from the first sealing station to the sealing means of the VFFS machine.
Yet another aspect of the invention is a method of sealing a zipper assembly to bag making film, the zipper assembly comprising first and second profiled closure members that are mutually interlockable, and first and second zipper flanges respectively connected to the first and second profiled closure members and projecting generally parallel to each other when the first and second profiled closure members are interlocked. The method comprises the following steps: (a) pressing a web of bag making film and the first and second zipper flanges of the zipper assembly together along the length of the latter, with the first zipper flange sandwiched between and in contact with the web of bag making film and the second zipper flange; and (b) during step (a), causing heat to be conducted through the web of bag making film into the first zipper flange, the amount of heat conducted through the web of bag making film being sufficient to seal the web of bag making film to the first zipper flange without sealing the first zipper flange to the second zipper flange.
Other aspects of the invention are disclosed and claimed below.